1. Field of the Invention
The present invention relates generally to systems for stabilizing the foundation of a building structure which may or has experienced settlement or movement and, more particularly, to an apparatus for stabilizing the foundation of a building against both settling and uplift forces.
2. Discussion of the Prior Art
It is known to provide a foundation underpinning bracket and jacking tool assembly for use in stabilizing the foundation of a building, wherein a support is positioned at the bottom of a foundation, a screw anchor is driven into the ground adjacent the support, a lifting force is applied to the foundation using the screw anchor as a base for the lifting force, and the support is thereafter received over the upper end of the screw anchor so that the live and dead loads of the foundation are transferred to the screw anchor. An example of such a method is illustrated in U.S. Pat. No. 5,120,163, issued Jun. 9, 1992 and U.S. Pat. No. 5,171,107, issued Dec. 15, 1992.
Prior to development of this noted method and the associated apparatus, it was conventional to drive a pile into the earth adjacent a foundation by exerting a driving force on the pile using the foundation as a base for the driving force. One problem experienced in these conventional pile supported systems and that was overcome in the '163 patent assembly, arose due to the fact that the piles were only driven into the earth until such time as the foundation began to lift as further driving force was applied to respective piles. However, the piles were subject to further subsequent penetration into the ground resulting in further settlement of the foundation.
The '163 patent method and assembly overcomes the problems in the earlier conventional systems by providing a screw anchor in place of each pile. Because the screw anchors are embedded through the use of a torque drive exerted on the screw anchors independently of the foundation, it is possible to install the anchors to a depth sufficient to support the live and dead load of the building structure without the occurrence of further settlement of either the anchors or the foundation.
Although the '163 patent assembly represents an improvement over other conventional systems in preventing settlement of the foundation of a building structure, there is a need to provide an improved method and apparatus which can also be used in areas where uplift forces are experienced, as for example by earthquake upheavals, to prevent uplift of the foundation. The problem of uplift arises during an earthquake when repeated wave-like upward and downward movement of the earth lifts the foundation from its settlement, allowing the foundation to shift laterally or to remain in an elevated position relative to the foundation's prior, final or settled position.